The construction industry often desires to employ excavations of various types, such as foundations, trenches, and the like. Where excavations are made in the earth, it is desirable to support the upright sidewalls of the excavation against collapse or to protect a sheltered work space in the event of collapse. While naturally the collapse of the sidewall will increase the costs of a project by requiring reexcavation, of greater concern is the potential danger of injury or death to workers construction project who are situated within the excavation. So great is the concern for worker safety, that some governmental agencies have promulgated regulations directed to the manner in which excavations are created and the structures used to support the excavations against sidewall collapse. The present invention is directed to laterally supporting the sidewalls of excavations, in general, and trenches, in particular and protecting in the event of collapse of unsupported excavation sidewalls. Technically, the positive supporting of a sidewall in this field is called "shoring" while the protection against collapse is called "shielding". These two possible implementations of the present invention may be jointly referred to as "buttressing", since, in some applications it may be desirable to employ the protective panel and shield system to shore an excavation sidewall, and in other applications it may be desirable to provide a shielded space in the event of collapse.
The desirability of supporting the sidewall of an excavation has long been known. Early structures used to buttress earthen sidewalls includes upright stone and wooden retaining walls, either alone or in combination with braces which extend between the retaining wall and a horizontal surface. These retaining walls, with or without the associated braces, resist lateral forces which tend to collapse or cause a cave-in of the sidewall.
Subsequently, shoring systems were developed wherein a plurality of upright sheeting members were placed against the sidewall of an excavation and were held in place by horizontal wales that were in turn braced either against the bottom of the excavation or, in trenching applications, against the opposed sidewall. Even more recently, prefabricated shoring systems usually referred to as "trench boxes" or "trench shields" have been manufactured for use in a variety of trenching or excavation applications.
One example of such a prefabricated trench box is shown in U.S. Pat. No. 4,090,365 issued May 23, 1978 to Nieber. In this structure, stackable side panels are outwardly disposed against an excavation and are cross-braced to prevent collapse of the trench. A portal frame is attached to the open end of the trench box in the form of an arch allowing clearance for a pipe to be laid in the trench. U.S. Pat. No. 4,202,649 issued May 13, 1980 to Cook et al. shows another trench box having a specially configured front plate. U.S. Pat. No. 4,259,028 issued Mar. 31, 1981 to Cook discloses a specially constructed trench box panel comprising a light-weight foam filler located between inner and outer panel surfaces in order to reduce weight and prevent leakage.
Despite the shoring structures developed in the past, several problems remain in virtually all such premanufactured assemblies. Primary among these problems is the low strength-to-weight ratio of the assemblies. That is, in order to obtain sufficient shoring strengths, fairly heavy support members, typically fabricated of steel, are used in structure. Due to the weight of these construction materials, the resulting trench boxes are unwieldy to insert and remove from the trench or excavation and often require the use of lifting machinery to manipulate the trench box. Furthermore, due to the weight of these structures, there is always an inherent danger of injury to a worker in the vicinity of the box during transport or positioning; repositioning or placement of such trench boxes is also very time consuming.
Accordingly, there remains a need for improved excavation shields and trench boxes which exhibit a high strength-to-weight ratio while providing adequate clearance for workers and equipment within an excavation. There is a further need for such shoring systems which are versatile and adaptable to a variety of buttressing needs and yet which are fast and easy to use without substantial risk or injury to the construction workers. The present invention is directed to meeting these needs, as described below.